As methods of treatment to be employed in the deposition of a diamond film by the vapor phase process on a hard metal substrate for the purpose of enhancing adhesive force between the deposited diamond film and the substrate, etching with a chemical substance such as an acid or an alkali (48th Scientific Lecture Meeting, 18a-T-4, Japan Applied Physics Society), scratching treatment with diamond powder (48th Scientific Lecture Meeting, 18a-T-5, Japan Applied Physics Society), and etching in a specific gas containing an alcohol (Japanese Patent Public Disclosure HEI 1-145396), etc. have been known to the art.
However, when, for example, a tool manufactured by forming a diamond film on hard metal lathe tip treated by one of these methods is actually used in cutting, the diamond film quickly exfoliates from the tip. Thus adhesive strength of a practical level cannot be obtained.
When a diamond film is formed on a hard metal substrate by the conventional method of surface treatment, the adhesive strength between the substrate and the diamond film is not sufficient. When the hard metal substrate coated with the diamond film is used as in cutting with a lathe, for example, this cutting work has the problem of ready exfoliation of the diamond film.
An object of this invention is to provide a method for the deposition of a diamond film with high adhesive strength on a hard metal substrate by the vapor phase process for the synthesis of diamond.